International projectionist (Jan 1963-June 1965)

Record Details:

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(Lateral movement only ; Costal QAAon autczL-^ crystal ^sStet^e ogh on i o^ FIG. 2 — The piezoelectric crystal of a monaural pickup is "twisted" in only one direction, the lateral direction parallel to the variations of the constant-depth groove. The crystal thus generates fluctuating sound currents. A stereo pickup works the same way, but it has two crystals positioned in planes 90 degrees apart. One crystal responds only to the variations in one wall of the record groove, and the other crystal responds only to the variations recorded in the other wall. Each crystal, accordingly, reproduces one of two separate channels of sound. DISC REPRODUCERS from page 7 average linear groove speed only 42.7% that of 78's. A slightly worn needle will distort the sound more badly on 33's than on 78's, while a severely worn needle may skip grooves, repeat grooves on overmodulated passages, and damage the record. Oscilloscopic tests which reveal distortion in highfrequency waveforms lead us to the conclusion that standard-groove 78-RPM records are best limited to 8000 cycles, while microgroove 33's cannot go much beyond 10,000 cycles without distortion. As a matter of fact, nothing in the way of audible "realism" is provided by frequencies higher than 10,000 cycles, which is more than twice as high-pitched as the highest note on a piano keyboard. Statements by recording companies (attempting 24,000 cycles) to the effect that excessively high frequencies add realism "even though they are not heard" are pure balderdash. Commercial amplifiers and speakers cannot reproduce 24,000 cycles; and few go up as high as 15,000 cycles. It has been said that only "bulldogs and babies" can hear up to 30,000 cycles. The average young adult 12 can probably hear sounds as high as 15,000 cycles, and in some cases up to 20,000. Sounds higher than 10,000 cycles are scarcely audible to anyone over 60 years of age. To a person who can easily hear 10,000 cycles, this extremely high-pitched tone sounds like a harsh whistling hiss totally devoid of timbre, or "tone color." It has no timbre because its harmonic (20,000 cycles, 30,000 cycles, and 40,000 cycles for the first three harmonics) are too high to be audible, even if really present. (The first three or four harmonics establish the general character of any tone — fluty, reedy, dull, piquant, etc.) A worn needle used on 33V3-RPM discs will distort the lower as well as the higher frequencies, and accentuate certain frequencies. Such a needle may skip grooves and damage the record. Sapphire and ruby needles have a relatively short life and, in general, are rather a nuisance with long-play records. Diamond needles have a useful life of 20 to 100 times the life of sapphire needles, and should be installed at the outset. Diamond needles cost only 4 or 5 times as much as the sapphire ones, and hence represent a real economy. Use Only All-Speed Stereo Players! This writer very strongly recommends the use of a combination-speed record player (16, 45, S3Ys, and 78 RPM) fitted with a flip-over cartridge, each side of which has its own needle. One side of the pickup plays 45 and 33% microgroove records, while the other side is for standard 78's. Be sure that the microgroove side of the cartridge is "stereo" no matter whether the noiv common stereo discs are reproduced monaurally or stereophonically! On account of the musical limitations of 45-RPM records, and the likelihood that this speed may be discontinued in favor of 33's for popular "singles," it seems best to concentrate exclusively on regular 12inch 33%-RPM long-play discs, both high-fidelity monaural and stereophonic. An ordinary monaural "lateral-cut" record has only sidewise variations of grooves of constant depth, but a dual-channel stereophonic record has two completely independent sets of variations in its grooves. One channel of sound is carried by lateral variations tilted 45° from the surface plane of the disc, while the other set of variations for the second channel is tilted 45° in the opposite direction. The two sets thus have a maximum angular separation of 90°. When the same sound is present in both channels, the angular difference of the plane of needle movement from the surface plane of the record is less than 45°, that is, 45° — n°, in which n is the angle of needle movement on the side of the groove (right or left sound channel) having the weaker signal. In the case of a regular monaural record played with a stereo pickup ( which improves the sound, by the way ) , the sidewise needle movement in the plane of the record surface is exactly the same as in a stereo record having identical signals of equal strength in both channels. (45° — 45° =0°.) The result is the same sound from the left and right speakers. To repeat: Stereophonic records are now so commonplace that the record player used in the theatre should be equipped with a stereo pickup cartridge no matter whether the sound is played monaurally through just one channel or stereophonically through two or three amplifier and speaker channels. International Projectionist January, 1963